THE MUSCLES AND FASCIA OF THE NECK. 313 



surface of the external pterygoid plate and to the grooved surface of the tuber- 

 osity of the palate bone, arid by a second slip from the outer surface of the 

 tuberosities of the palate and superior maxillary bones ; its fibres pass downward, 

 outward, and backward, to be inserted, by a .strong, tendinous lamina, into the 

 lower and back part of the inner side of the ramus and angle of the lower jaw, 

 as high as the dental foramen. 



Relations. By its external surface, with the ramus of the lower jaw, from 

 which it is separated, at its upper part, by the External pterygoid, the internal 

 lateral ligament, the internal maxillary artery, the dental vessels and nerves, and 

 the lingual nerve, and a process of the parotid gland. By its internal surface, 

 with the Tensor palati, being separated from the Superior constrictor of the 

 pharynx by a cellular interval. 



Nerves. These muscles are supplied by the inferior maxillary nerve. 



Actions. The Temporal and Masseter and Internal pterygoid raise the loAver 

 jaw against the upper with great force. The superficial portion of the Masseter 

 assists the External pterygoid in drawing the lower jaw forward upon the upper, 

 the jaw being drawn back again by the deep fibres of the Masseter and posterior 

 fibres of the Temporal. The External pterygoid muscles are the direct agents in 

 the trituration of the food, drawing the lower jaw directly forward, so as to fnake 

 the lower teeth project beyond the upper. If the muscle of one side acts, the 

 corresponding side of the jaw is drawn forward, and, the other condyle remaining 

 fixed, the symphysis deviates to the opposite side. The alternation of these 

 movements on the two sides produces trituration. 



Surface Form. The outline of the muscles of the head and face cannot be traced on the 

 surface of the body, except in the case of two of the masticatory muscles. Those of the head 

 are thin, so that the outline of the bone is perceptible beneath them. Those in the face are 

 small, covered by soft skin, and often by a considerable layer of fat, so that their outline is con- 

 cealed, but they serve to round off and smooth prominent borders and to fill up what would be 

 otherwise unsightly angular depressions. Thus, the Orbicularis palpebrarum rounds off the 

 prominent margin of the orbit, and the Pyramidalis nasi fills in the sharp depression beneath 

 the glabella, and thus softens and tones down the abrupt depression which is seen on the 

 unclothed bone. In like manner, the labial muscles, converging to the lips and assisted by the 

 superimposed fat, fill in the sunken hollow of the lower part of the face. Although the muscles 

 of the face are usually described as arising from the bones and inserted into the nose, lips, and 

 corners of the mouth, they have fibres inserted into the skin of the face along tlieir whole 

 extent, so that almost every point of the skin of the face has its muscular fibre to move it ; 

 hence it is that when in action the facial muscles produce alterations in the skin-surface, 

 giving rise to the formation of various folds or wrinkles, or otherwise altering the relative 

 position of parts, so as to produce the varied expressions with which the face is endowed ; 

 hence these muscles are termed the "muscles of expression." The only two muscles in this 

 region which greatly influence surface form are the Masseter and the Temporal. The Masseter 

 is a quadrilateral muscle, which imparts fulness to the hinder part of the cheek. When the 

 muscle is firmly contracted, as when the teeth are clenched, its outline is plainly visible ; 

 the anterior border forms a prominent vertical ridge, behind which is a considerable fulness, 

 especially marked at the lower part of the muscle; this fulness is entirely lost when the 

 mouth is opened and the muscle no longer in a state of contraction. The Temporal muscle 

 is fan-shaped, and fills the Temporal fossa, substituting for it a somewhat convex form, 

 the anterior part of which, on account of the absence of hair over the temple, is more 

 marked than the posterior, and stands out in strong relief when the muscle is in a state of con- 

 traction. 



MUSCLES AND FASCLflE OF THE NECK. 



The muscles of the neck may be arranged into groups corresponding with the 

 region in which they are situated. 



These groups are nine in number : 



1. Superficial cervical region. 5. Muscles of the Pharynx. 



2. Depressors of the Os Hyoides 6. Muscles of the Soft Palate. 



and Larynx. 7. Muscles of the Anterior Ver- 



3. Elevators of the Os Hyoides tebral Region. 



and Larynx. 8. Muscles of the Lateral Ver- 



4. Muscles of the Tongue. tebral Region. 



9. Muscles of the Larynx. 



